Inexpensive bi-axial sun tracker for solar concentrators

ABSTRACT

A relatively simple, inexpensive, and easily manufactured device for accurately tracking the daily and seasonal movement of the sun anywhere, and in any climate, without the need for human and/or computer intervention. This sun tracker can be made to any size, out of common materials, and using standard assembly line techniques. Said sun tracker can be installed for any application by an unskilled person. Once installed, it will use a simple electro-mechanical configuration instead of a complex mechanical or costly computer control, as all prior art required.

CROSS REFERENCE TO RELATED APPLICATIONS

PPA filed Sep. 18, 2009 Ser. No. 61/277,014

FEDERALLY SPONSORED RESEARCH

NONE

SEQUENCE LISTING

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BACKGROUND

This application relates to sun trackers, which are used to increase theoutput of solar cells. The idea of producing electricity from the sunhas been around for over one hundred years. While the efficiencies ofsolar cells continue to rise, they remain costly to produce. Recently,an attempt has been made to lower the cost of solar power byconcentrating the sun's rays onto a solar collector. This concentratedsunlight can then be either converted directly into electricity by asolar cell, or be used to boil water and drive a turbine. This, however,presents a new challenge. For solar concentrators to work, some means ofaccurately tracking the sun must be employed. Unfortunately, all knownmethods compromise cost, accuracy, and complexity.

For example, U.S. Pat. No. 4,027,651 to Ronald W. Robbins, Jr. (1977)uses an opaque divider between two sets of liquid-filled coils.Whichever set received more radiation gets hotter, the liquid boils, andthe solar cells move in that direction. Although simple, it could notdeliver a high degree of accuracy because of the large temperaturedifference needed. Also, it could not be used in extreme climates. Othermethods provide more accuracy, but tend to me complex and costly. U.S.Pat. No. 5,600,124 to Alexander Berger (1997) was able to bypass airtemperature problems, but needed a complex mechanical drive to operate.For large scale energy production, fields of mirrors have been used toconcentrate sunlight onto a solar tower. The concentrated light boiledwater and drove a turbine. However, every individual mirror needed itsown precise path, which was controlled by a complex and costly computerprogram.

The cost of fossil fuels continues to rise, and easy sources arebecoming harder to find. We are already running out of options otherthan to extract them from environmentally and politically sensitiveareas. Unless a practical alternative is found and utilized soon,widespread habitat destruction and political confrontations(wars) arelikely in these areas. Every day, enough sunlight strikes the earth'ssurface to supply mankind's energy needs for hundreds of years. Clearly,an effective means of harnessing the sun's extreme power is needed.

SUMMARY

A simple, portable, low-cost, and user-friendly device for accuratelytracking the sun. It uses no exotic materials, and can be used anywhere.It can be made to a wide range of sizes, suiting virtually any demand.

The daily movement of the sun is sensed by individual cells which arearranged in a semi-circular pattern. Each cell contains a simple devicethat senses the temperature difference between sun and shade. When acell is activated by sunlight, it closes an electrical circuit to rotatea solar concentrator from east to west. The seasonal movement of the sunfrom high to low in the sky is sensed by a separate device on the sameunit. This sensor operate on the same principle as the beforementionedcells, except that it rotates up and down with the seasonal sun andkeeps the solar concentrator at the same angle

The sun tracker uses a simple electro-mechanical system of rotatingwheels and electrical contacts, eliminating the need for an operator orcomputer system while providing a high degree of accuracy. This suntracker can also be made on an assembly line using common materials andtechniques, making it available to the general population.

DRAWINGS

FIG. 1A is a side cross-section view of a Solar Responsive Cell, whichis used to track the sun on its daily movement from east to west.

FIG. 1B is a top view of an SRC

FIG. 1C is a top view of the inner workings of an SRC

FIG. 1D is a front cross-section view of an SRC

FIG. 2A is a side cross-section view of a Sun Angle Sensor, showing itsinner workings and outside electrical contacts

FIG. 2B is a front cross-section view of the SAS

FIG. 2C is a side view of an SRC adjacent to the SAS, showing metalplates

FIG. 3 shows entire tracking unit, with SRC mounts and SAS in place

FIG. 4A is a side view of concentrator assembly

FIG. 4B is a top view of concentrator assembly base, showing electricalcontacts and motor

FIG. 4C is a bottom view of heavy-duty wheel to which solar concentratoris mounted

FIG. 4D is a top view of concentrator assembly

FIG. 4E is an enlarged top view of seasonal motor, seasonal gear, andcontrol rod

FIG. 4F is a view of seasonal motor without seasonal gear, showing itselectrical contact

FIG. 5 shows the electrical diagram for sun tracker

DRAWINGS Reference Numerals

10 solar responsive cell 11 SRC black strip 12 SRC bare strip 13 SRCelectrical contact 14 SRC housing 15 slit 16 SRC supports 17 shadingshelf 18 rails 200 sun angle sensor 201 SAS black strips 202 SAS barestrips 203 SAS strip contacts 204 SAS housing 205 lens 206 SAS supports207 axle stud 208 gear 209 SAS motor 210 SAS contacts 211 adjacent SRCplates 30 disk 31 rod 32 column 33 hex nut 34 SRC mounts 401 base 402base contacts 403 base motor 404 wheel 405 wheel plates 407 hinge 408solar concentrator 409 seasonal motor 410 seasonal gear 411 control rod412 seasonal gear contacts 413 seasonal motor contact 50a, b, c, drechargeable batteries

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1A shows two identical bi-metallic strips placed side by side. Bothare bent to form a long U-shape. The top half of one is paintedblack(11), and the other is left bare(12). Said bare strip has anelectrical contact(13) that extends toward and just below the end ofsaid black strip.

These two bi-metallic strips are encased inside of a housing(14) thatcompletely encases them, except for a slit(15) in the top(FIG. 1B). Saidslit is parallel to said black strip and runs across the top of saidhousing. Both said strips are attached to supports(16) underneath themso that the tops of said strips are immobilized, while their bottoms arefree to move up and down. Said slit is covered by a transparentmaterial, such as glass or plastic.

FIG. 1C shows a shelf(17) that extends from the side of said housingthat completely shades said bare strip so that it cannot be seen throughthe slit at any angle. The entire top half of said black strip can beseen through slit. Said housing has two long rails(18, FIG. 1D)extending along either side of the bottom so that it can be attached toa mount(34) on a tracking unit. Said housing containing said black andbare strips shall be referred to as a Solar Responsive Cell, or SRC(10).

FIG. 2A shows a modified SRC. Four bi-metallic strips are bent into aU-shape and set side by side in the same way as the beforementioned SRCstrips. The middle two said strips(201) are painted black, while theoutside two(202) are bare. Each bare strip has an electricalcontact(203) extending toward and just below adjacent black strip. Thereis a housing(204) around these four strips, just like in said SRC. Thetop of said housing has a lens(205) positioned so that the focal pointis in the space between the tops of said black strips. The width of thearea of concentrated sunlight in the space between said black strips isno greater that the width of the space itself. As in said SRC, all saidstrips have a support(206) underneath their top halves. This unit shallbe referred to as a Sun Angle Sensor, or SAS(200).

At the center of each side of SAS housing perpendicular to SAS stripsthere is an axle stud(207) which sticks out from unit. Underneath SAS isa toothed gear(208) which covers no less that 47 degrees of arc, andcenters on a line drawn between said axle studs. Said gear isperpendicular to direction of said SAS strips. There is a motor(209)underneath said gear which rotates very slowly.

On one side of the SAS that has an axle stud, there is a series ofelectrical contacts(210) which are arranged in a semicircle. Saidsemicircle takes up 47 degrees of arc and all contacts are equidistantfrom said axle stud. FIG. 2C shows the side of an SRC which shall beadjacent to said SAS on the side with the contacts. There are two metalplates(211) that are identical to each other and take up the same arc asthe beforementioned SAS contacts. There is a gap between said plateswhich is equal to the width of two SAS contacts.

FIG. 3 shows the complete tracking unit. There are many SRC mountsarranged in a semicircle on the outside of a disk(30). Said disk isbisected vertically and the SAS is placed between the two halves, facingup. Said SAS rotates on its axle studs. At the center of each of theinside surfaces, there is a hole. A rod(31) runs between said diskhalves and into both holes. Said rod is supported by a column(32) whichgoes into the ground. Said rod is fixed to column so that it cannotrotate in relation to the column. Between said column and said diskhalves, said rod is threaded and a hexagonal nut(33) is placed on bothsides of the rod.

FIG. 4A shows the concentrator assembly. The assembly begins with acircular base(401). In the center of said base there is a hole intowhich a slowly rotating motor(403) is placed. This motor shall bereferred to as the base motor. Its axle is perpendicular to the base andpoints upward. A heavy-duty wheel(404) is mounted on the axle of saidbase motor. Heavy-duty wheel shall be referred to simply as the wheel.There is a hinge(407) attached to the outside of said wheel whichrotates on an axis tangent to said wheel. Solar concentrator(408) isattached to said hinge so that it can rotate no less that 23.5 degreesin both directions. There is another motor(409) which sits on its sideon top of wheel this motor shall be referred to as the seasonal motor.The axle of said seasonal motor is parallel to solar concentrator. Thereis a seasonal gear(410) which is set vertically, perpendicular to solarconcentrator, and intersects with a small gear on the axle of seasonalmotor. At the top of seasonal gear there is a hole into which a controlrod(411) is riveted. Said rod is then attached to a point on solarconcentrator so that rod is parallel to wheel. Said rod is not fixed ateither end and remains parallel to wheel when concentrator and seasonalgear are rotated back and forth. There are electrical contacts(412)along 23.5 degrees of seasonal gear on either side of the point which isin contact with seasonal motor axle when the solar concentrator isperpendicular to wheel. There is one electrical contact(413) on seasonalmotor which is the same width as each seasonal gear contact.

FIG. 4B shows the top of said base. There is a series of electricalcontacts(402) arranged in a complete circle around said base. There areas many contacts as the maximum number of SRC's the tracking unit canaccommodate. FIG. 4C shows the underside of said wheel. There are twoidentical metal plates(405) which completely encircle wheel except for agap between them on both ends. These gaps are slightly wider than onebase contact, and a line drawn through the center of the wheel and thecenters of the gaps is parallel to beforementioned rod.

FIG. 5 shows the electrical wiring of the preferred embodiment. Fourrechargeable batteries(50 a,b,c,d) supply the power for the system. Saidbatteries shall be labeled A, B, C, and D. the positive terminal onbattery A is wired to one terminal on base motor. The negative terminalon battery A is wired to each SRC bare strip. The positive terminal onbattery B is wired to the base motor terminal not beforementioned. Thenegative terminal on battery B is wired to the negative terminal onbattery A. Each SRC black strip is wired to one contact on base of solarconcentrator. The next SRC black strip going west is wired to the nextbase contact going counterclockwise (clockwise if unit is being used insouthern hemisphere), and so on. One wheel plate is wired to terminal onbase motor; the other wheel plate is wired to the other base motorterminal.

The positive terminal on battery C is wired to one bare strip on SAS andone terminal on seasonal motor. The negative terminal on battery C iswired to one terminal on SAS motor an done plate on adjacent SRC. Thepositive terminal on battery D is wired to SAS bare strip notbeforementioned. The negative terminal on battery D is wired to positiveterminal on battery C and SAS motor terminal not beforementioned. EachSAS contact is wired to a corresponding contact on seasonal gearseasonal motor contact is wired to seasonal motor terminal notbeforementioned.

OPERATION OF THE PREFERRED EMBODIMENT

Tracking unit is placed with the SAS pointing directly upward, and SASstuds point due east/west. Entire unit is then rotated, with SAS movingtowards the earth's equator, the number of degrees as the latitude unitis being used at. For example, let's assume the sun tracker is beingused in the District of Columbia, latitude 38.85° N. Looking east,tracking unit will be rotated clockwise from vertical just short of 39degrees. Unit is then locked in place by tightening the hex nuts onsupporting rod. Then SRC's are placed onto the unit so that they coverat least as much as fifteen degrees for every hour of sunlight on thesummer solstice. Thus, in D.C., enough SRC's will be placed on the unitto cover 255 degrees for fifteen hours of daylight. SAS is then adjustedso that light beam falls between SAS black strips.

Concentrator assembly is then mounted so that the plane of the wheel isat the same angle to the ground as the tracking unit. A line drawn fromthe center of said wheel through the center of a wheel contact wouldpoint to the same point in space as a line drawn from the center oftracking unit through the center of said wheel contact's correspondingSRC. Concentrator assembly is mounted far enough off of the ground orother supporting structure so that concentrator assembly can rotate 360degrees and solar concentrator can rotate 23.5 degrees up and downwithout hitting any solid object. Electrical wiring is then completed tothe batteries. As this is done, electricity will run through SAS circuitand move concentrator so that it is at the same angle as the sun. If thesun is not shining already, when it does so next, it will shine on theblack strip in one SRC. The strip will absorb radiation, heat up, andbend due to its bi-metallic nature. When it has bent enough to tough thecontact on the bare strip beside it, an electrical circuit is completedthrough the SRC, its corresponding base contact, wheel plate, and basemotor. Concentrator assembly then rotates until the gap between the twoplates is centered above the energized base contact. Circuit is broken,and the solar concentrator is now pointed directly at the sun.

As the sun moves from east to west, its light will move off of the blackstrip it was before shining on. The sun will now be in direct alignmentwith the next SRC black strip going west, and an electrical circuit iscompleted through the next base contact. Concentrator assembly rotatesuntil gap between plates is aligned with the newly energized basecontact and stops. If the sun has not been shining for at least twelvehours, as is the case with a winter night or a considerably cloudysummer day, the energized base contact will then be touching the otherwheel plate. The circuit through this plate is wired so that electricityflows the opposite way through base motor. Concentrator assembly willthen move from west to east because that would be the shorter path torealignment with the sun. as the weeks go by, the sun will change itsangle with the horizon. As the noon sun gets lower or higher in the sky,the beam shining through the lens in the SAS will move onto one of theblack strips. When enough light is shining on this black strip, it willheat up and tough the contact on the bare strip beside it. An electricalcurrent is completed through the SAS motor, and SAS slowly rotates inthe direction of the sun. As SAS rotates, sunlight moves off of thestrip it was shining on. Strip cools down, breaks the circuit, and SASstops. As SAS rotates, its contacts move along the adjacent SRC strips.When SAS has moved enough so that the SAS contact which corresponds tothe seasonal gear contact touching the seasonal motor contact nowtouches an SRC plate, an electrical circuit is completed through theseasonal motor. Concentrator will move vertically until the newlyenergized seasonal gear contact moves off of the seasonal motor contact.Circuit is broken, and solar concentrator is now seasonally adjusted.

When the sun reaches a solstice and moves in the opposite seasonaldirection, the SAS black strip not beforementioned will receive theradiation, heat up, and close a circuit in which electricity flows inthe opposite direction through the SAS motor. SAS moves in oppositedirection, as does the concentrator.

CONCLUSION, RAMIFICATIONS, AND SCOPE

As can be seen, at least one embodiment of this sun tracker providesaccurate tracking of the sun on a daily as well as a seasonal basiswithout the need for an operator, complex mechanical, or costly computercontrol. No device currently in existence can accomplish this. It can beused in any climate, anywhere on Earth. With simple modifications to thelengths of the tops of the SRC's, this sun tracker can even be used onextra-terrestrial surfaces. Also, one tracking unit can be wired inparallel to a virtually unlimited number of concentrators, furthersimplifying use.

Although my description and drawings contain many things, many areirrelevant to the specific technology I have invented. They only showone way of using it, and therefore should not be used to limit thescope. My invention should be defined by the following claims, and notby the preceding description. For example, contained fluids may be usedinstead of bi-metallic strips. The tracking unit may be immobilized byclips instead of nuts. Concentrating lenses may be used in the SRC gapsto further increase accuracy.

1. A device containing pairs of temperature sensors, one shaded and theother exposed to light, arranged in a circular pattern to track the sunfor a solar collector by: a. Detecting a temperature difference betweensaid sensors and inducing an electrical current which moves said solarcollector, and b. Stopping said electrical current when said solarcollector is pointing directly at said sun.